The Dark-Ages 21-cm Trough near Redshift Eighty: A Bounce-Invariant Prediction

Between the epoch when the gas thermally decouples from the radiation and the epoch when the first stars switch on, the hydrogen signal is at its cleanest. Using the stated cosmology and the brightness-temperature relations described in the Methods, the calculation gives the following headline values: z = 80; depth mK = -67; Tg K = 118.0; Tcmb K = 221. The comparison values taken from the published record — including the EDGES and SARAS reports, HERA limits and the Planck optical depth where relevant — are used exactly as published, and the bounce contribution enters only through the named timing, heating or shear inputs. The result is a computed prediction for the delayed-onset history, with its sensitivity to each input stated in the Discussion. This study is simulated and computed from stated assumptions; it is not a measurement.